1. Field of the Invention
The present invention relates to an image-forming device such as a laser printer, and a cartridge detachably mounted in the image-forming device.
2. Description of the Related Art
Some conventional electrophotographic image-forming devices such as laser printers include a developer cartridge that is detachably mounted in the image-forming device. A toner-accommodating chamber for accommodating toner is formed in the developer cartridge. In this type of image-forming device, the developer cartridge is replaced when the toner accommodated in the toner-accommodating chamber has been consumed. To this end, the image-forming device includes a residual toner detecting device for detecting the amount of toner remaining in the toner-accommodating chamber.
One such residual toner detecting device for an image-forming device has been proposed in U.S. Pat. No. 6,337,956. This image-forming device includes a developing device having a toner-accommodating chamber. Light-transmitting windows are provided on both side walls of the chamber in the widthwise direction. The residual toner detecting device includes a light-emitting element and a light-receiving element disposed so that the optical axis of light emitted from the light-emitting unit passes through the light-transmitting windows in both side walls of the toner-accommodating chamber.
In this conventional image-forming device, the residual toner detecting device determines the amount of residual toner in the toner-accommodating chamber with the light-emitting element and the light-receiving element disposed in opposition to each other on opposite sides of the toner-accommodating chamber to detect whether a detection light emitted from the light-emitting element passes through the toner-accommodating chamber and is received by the light-receiving element.